Multi-array pencil-sized ultrasound transducer and method of imaging and manufacture

ABSTRACT

An ultrasound transducer having a field of view greater than 180°, and having a physical shape which permits it to be employed in the investigation and observation of the anatomy, or other body, object or region of interest, having limited access. A plurality of ultrasound transducer arrays are provided, each having a field of view defining an image plane, wherein the axis of each transducer array lies within its corresponding defined image plane. Preferably, the plurality of transducer arrays are positioned end-to-end and nonaxially aligned with the image planes of all transducer arrays coincident, and with each transducer array having a field of view of about 90°, whereby a resulting combined field of view greater than 90° is produced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to ultrasound transducers, and more particularlyto phased array ultrasound transducers for use particularly in themedical and diagnostic fields.

2. Brief Description of the Prior Art

Ultrasound machines are widely used for observing internal organs in thehuman body. Physically, these machines contain ultrasound transducerarrays for converting electrical signals into acoustic pressure wavesand vice versa. Generally, the ultrasound transducer array is in theform of a hand-held probe which may be positioned and oriented to directthe ultrasound beam to the region of interest.

The size and limited field of view of existing general purposeultrasound transducers limit their utility in surgical applications andin applications in which the transducer probe must be inserted into abody cavity. There are regions in the anatomy that cannot be reachedusing general purpose transducers, and in those regions that can bereached, the field of view is limited to about 90°.

Thus, it is desirable to provide an ultrasound transducer probe that hasa field of view greater than existing ultrasound transducers. It is alsodesirable to provide an ultrasound transducer having dimensions thatallow it to be used in surgical and diagnostic applications where thereis limited access.

SUMMARY OF THE INVENTION

The present invention fulfills the need in the art for an ultrasoundtransducer having a field of view greater than 90°, and having aphysical shape which permits it to be employed in the investigation andobservation of the anatomy, or other body or object, having limitedaccess.

In accordance with the invention, there is provided a plurality ofultrasound transducer arrays, each having a field of view defining animage plane, wherein the axis of each transducer array lies within itscorresponding defined image plane.

Preferably, the plurality of transducer arrays are nonaxially alignedand positioned end-to-end with the image planes of all transducer arrayscoincident, and with each transducer array having a field of view ofabout 90°, whereby a resulting combined field of view greater than 90°is produced.

The ultrasound transducer assembly may comprise a housing with a firsttransducer array arranged at the tip of the housing distal end foracquiring an ultrasound image forward of the distal end, and a secondtransducer array arranged on a side of the housing distal end foracquiring an ultrasound image laterally of the distal end. The inventionmay comprise more than two transducer arrays for acquiring ultrasoundimages in a variety of selectable directions.

More particularly, the invention may comprise an elongated pencil-sizedhousing having distal and proximal ends, a first transducer arrayarranged adjacent the housing distal end for acquiring an ultrasoundimage in a first image plane and with a first field of view of about90°, and a second transducer array arranged adjacent the housing distalend for acquiring an ultrasound image in a second image plane and with asecond field of view of about 90°, the first image plane being coplanarwith the second image plane, and the second field of view overlappingthe first field of view, resulting in a combined field of view of about180°.

The proximal end of the pencil-sized housing may be attached to a cable,the cable being connected internally to the first and second transducerarrays, the other end of the cable being connected to a multi-contactconnector for attachment to an ultrasound system console. Alternatively,the ultrasound transducer assembly may have a contact terminal, or plug,at its proximal end which is insertable into a hand-held receptacle, thereceptacle being connected to the ultrasound system console through amulti-conductor cable.

Methods of manufacture for various preferred embodiments of theinvention will be described.

BRIEF DESCRIPTION OF THE DRAWING

These and other aspects of the invention will be better understood, andadditional features of the invention will be described hereinafterhaving reference to the accompanying drawings in which:

FIG. 1 is a schematic block diagram of an ultrasound system forgenerating an image of an object or body being observed;

FIG. 2 is a perspective side view of one embodiment of the invention inwhich the pencil-sized ultrasound transducer is attached to the end of amultiple coaxial conductor cable leading to an imaging system console;

FIG. 3 is a top view of the end of the ultrasound transducer shown inFIG. 2 depicting the field of view patterns produced;

FIG. 4 is a perspective view of a receptacle assembly attached to amultiple coaxial conductor cable leading to the imaging system console;

FIG. 5 is a perspective view of a pencil-sized ultrasound transducermodule receivable in the receptacle assembly of FIG. 4 attached to acable leading to the imaging system console;

FIG. 6 is a side view of the ultrasound transducer module shown in FIG.5;

FIG. 7 is a top view of the ultrasound transducer module shown in FIG.5, with the distal end of the transducer module shown in partial crosssection;

FIG. 8 is a cross sectional view of the end of an ultrasound transducerprobe of the present invention seen in FIG. 6 showing an arrangement offront and lateral looking bi-stack transducer arrays;

FIG. 9 shows a flexible circuit connected to the lateral lookingacoustic transducer subassembly;

FIG. 10 is a right side view of the lateral looking acoustic transducersubassembly as shown in FIG. 9;

FIG. 11 is a back side view of the lateral looking acoustic transducersubassembly as shown in FIG. 9;

FIG. 12 shows a flexible circuit connected to the front looking acoustictransducer subassembly;

FIG. 13 is a right side view of the front looking acoustic transducersubassembly as shown in FIG. 12;

FIG. 14 is a back side view of the front looking acoustic transducersubassembly as shown in FIG. 12;

FIG. 15 is a view showing the assembly of both the front and laterallooking acoustic transducer subassemblies;

FIG. 16 is a left side view of the combined front and lateral lookingacoustic transducer subassemblies of FIG. 15;

FIG. 17 is a cross sectional view of an intermediate portion of thepencil-sized transducer module taken along the lines 17--17 in FIG. 2;

FIGS. 18-21 illustrate an interconnection scheme for the termination ofcoaxial conductors to a printed wiring board within the pencil-sizedtransducer as shown in FIG. 2, FIG. 18 showing the coaxial conductorinterconnect side of the printed wiring board;

FIG. 19 shows the flex circuit interconnect side of the printed wiringboard of FIG. 18;

FIG. 20 is a fragmentary perspective view of the interconnectionsbetween the printed wiring board of FIG. 19 and a flex circuit leadingto one of the transducer arrays;

FIG. 21 is a fragmentary perspective view of the termination of coaxialconductors to the printed wiring board of FIG. 18 within thepencil-sized ultrasound transducer housing;

FIGS. 22-27 illustrate an interconnection scheme for interconnecting theflex circuits leading to the transducer arrays, with the printed wiringboard leading to the transducer interconnect extension, or plug, for thepencil-sized transducer module shown in FIG. 5, FIG. 22 showing thecontact pad side of the printed circuit board and the connected flexcircuit from the lateral looking transducer array;

FIG. 23 is a side view of the arrangement shown in FIG. 22;

FIG. 24 shows the back side view of the plug and the connected flexcircuit leading to the front looking transducer array;

FIG. 25 is a view similar to that of FIG. 22 with the flex circuit andlateral looking transducer array removed;

FIG. 26 is a view similar to that of FIG. 23 with the flexible circuitsand both lateral and front looking transducer arrays removed;

FIG. 27 is a view similar to that of FIG. 24 with the flex circuit andfront looking transducer array removed;

FIG. 28 is a partial cross sectional view of a front looking bi-stacktransducer;

FIG. 29 shows one of the flex circuit and transducer array subassembliesfor the front looking bi-stack transducer shown in FIG. 28;

FIG. 30 is a back side view of the flex circuit and transducer arraysubassembly shown in FIG. 29;

FIG. 31 is a partial cross sectional view of a front looking tri-stacktransducer;

FIG. 32 shows one of the flex circuit and lateral looking transducerarray subassemblies for the front looking tri-stack transducer shown inFIG. 31;

FIG. 33 is a right side view of the lateral looking transducer arraysubassembly shown FIG. 32;

FIG. 34 is a back side view of the flex circuit and lateral lookingtransducer array subassembly shown in FIG. 32;

FIG. 35 shows the flex circuit and front looking transducer arraysubassemblies for the front looking tri-stack transducer shown in FIG.31;

FIG. 36 is a left side view of the front looking transducer arraysubassembly shown FIG. 35;

FIG. 37 is a back side view of the flex circuit and front lookingtransducer array subassembly shown in FIG. 35;

FIG. 38 is a circuit block diagram showing functional blocks forgenerating an image on a display using a transducer having more than onetransducer array stack;

FIG. 39 shows, schematically, the sequence and spacial positions oftransmitted acoustic beams from a transducer with front and lateraltransducer stacks; and

FIG. 40 shows, schematically, the interception of acoustic energyreflected from an object, by both transducer stacks of a bi-stacktransducer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic block diagram of an ultrasound system 1 forgenerating an ultrasound image of an object or body 10 being observed.The ultrasound system 1 includes a system console 12 containing transmitcircuitry 2 for transmitting electrical signals to an ultrasoundtransducer probe 4, receive circuitry 6 for processing signals receivedby the ultrasound transducer probe 4, and a display 8 for providing avisual image of the object or body 10 being observed. A multiple coaxialconductor cable 14 connects the ultrasound transducer probe 4 to thesystem console 12 via a system connector 28.

FIG. 2 depicts one embodiment of the invention in which an imagingpencil-sized ultrasound transducer probe 18 is permanently attached tothe end of a multiple coaxial conductor flexible cable 14 leading to theimaging system console 12. Elastomeric strain reliefs 24 and 26 aresupplied at the probe end and console end, respectively, of the multiplecoaxial conductor cable 14. The system end of the cable 14 is connectedto a system connector 28 which is mechanically and electrically coupledto the system console 12 by manipulating a locking actuator 30 of knowndesign, such as the ITT Cannon "DL" Series.

The pencil-sized transducer probe 18 is shown to have a pair of imagingphased transducer array stacks 46 and 48 positioned at the distal end ofthe transducer probe 18, the phased array stack 46 forming an imagingplane of generally trapezoidal shape toward the distal end of thetransducer probe 18, and phased array stack 48 producing a laterallooking imaging plane of generally trapezoidal shape, the image planesfrom both transducer stacks lying in a common imaging plane 22.

The formation of the combined imaging planes from the two imagingultrasound transducer array stacks 46 and 48 is best observed byreference to FIG. 3 which is a fragmentary top plan view of the end oftransducer probe 18 shown in FIG. 2. In FIG. 3, the image plane fromstack 46 has an approximate 90° field of view 41 forwardly of the probe18, while the transducer array stack 48 produces a laterally directedimagine plane having a field of view 43 of approximate 90° and slightlyoverlapping with the field of view 41 from the front looking array stack46.

The individual transducer elements of each of the transducer arrays46,48 on the front and lateral stacks can be electrically excited withdifferent amplitude and phase characteristics to steer and focus theultrasound beam. An example of a phased array acoustic imaging system isdescribed in U.S. Pat. No. 4,550,607 issued Nov. 5, 1985 to Maslak etal. and is specifically incorporated herein by reference. U.S. Pat. No.4,550,607 illustrates circuitry for combining the incoming signalsreceived by the transducer array to produce an image on the displayscreen.

The ultrasound transducer probe of the present invention can be usedwith existing microcode to provide images from the front or images fromthe side of the probe. The probe would operate as two separateindependent transducer devices in a single housing. However, theultrasound system can be reprogrammed so that both the front and sideimages can be displayed simultaneously. Because simultaneous operationof both stacks may present problems, the stacks may be firedalternately.

A wide family of transducer stacks can be utilized to implement thepresent invention, including linear arrays, trapezoidal imaging arrays,and curvilinear arrays. In a preferred embodiment, trapezoidal sectorimaging format is used for each transducer array stack, whereby thefield of view from the phased array stack may even exceed 90°. Employingthe construction and concepts of U.S. Pat. No. 4,550,607, the field ofview may even extend to approximately 110°. For purposes of illustrationin this description, however, some phased array stacks will be showngraphically to represent approximately a 90° field of view, and withsome slight overlap, the combined field of view will be shown to beslightly less than 180°. Other figures will show greater than 90° fieldsof view resulting in greater than 180° when combined. Other embodimentswill be described which may produce a field of view exceeding 270°.

This extended field of view, well beyond the normal 90°, improves theutility of the transducer probe in surgical applications, and has theadded benefit of providing the surgeon or technician with visual imagingof areas adjacent a particular point of interest without having to movethe probe and disturb the environment of investigation or cause thepatient discomfort. The details of construction and method ofmanufacturing assembly for a multiple array pencil-sized ultrasoundtransducer assembly will be described in further detail.

FIG. 4 is a perspective view of a cable assembly 17 connected to anultrasound imaging system console 12. The cable assembly 17 includes acable 14, a system connector 28 at one end, and a receptacle 40 at theother end.

FIG. 5 shows a preferred embodiment of a transducer probe module 34having a coupling plug member 36 which allows the probe module 34 to becoupled to the receptacle 40 of the cable assembly 17. The coupling plugmember 36 (hereinafter, plug) has a number of electrical contact pads 38(schematically represented) on a flat surface thereof which couple tocorresponding electrical contacts (not shown) in the body of receptacle40. Coupling member 36 is shaped to be received in a receptacle slot 40ain the end of receptacle 40, and an actuation lever 39 is provided toelectrically and mechanically connect the transducer probe module 34 tothe receptacle 40 by pushing down on the actuator lever. Details of anappropriate receptacle assembly for implementing this preferredembodiment of the invention can be found by reference to U.S. Pat. No.5,617,866 entitled "Modular Transducer System". Details of the couplingmember 36 will be described in greater detail hereinafter.

Using the plug and receptacle approach as shown in FIGS. 4 and 5,transducer assemblies with different imaging characteristics can bequickly and conveniently installed into the receptacle during diagnosticprocedures. Additionally, the removable probe module 34 may besterilized without having to sterilize the entire cable assembly 17.

Generally, an ultrasound imaging system is not located in the sterileenvironment of the operating room. Another advantage of a transducerprobe being removable from a receptacle 40 and cable assembly 17 asshown is that the transducer probe 34 can be changed in the sterileenvironment of the operating room remotely from the ultrasound system.Additionally, being modular, the transducer probe module 34 may beinterchanged with another type of transducer probe module using the samecable assembly 17, the same cable connections to the system console, andthe same ultrasound system.

Strain reliefs 24 and 26 are provided at the ends of cable 14 as thecable 14 enters the receptacle 40 and system connector 28, respectively.A system connector locking actuator 30, of known design, locks thesystem connector 28 to the imaging system console 12 mechanically andelectrically.

At the distal end of transducer probe module 34, and in accordance withone preferred embodiment of the invention, a front looking transducerimaging subassembly 46 is located at the distal end of the probe module34, while a similar transducer imaging subassembly 48 is shown to belocated laterally of the distal end of the probe module 34. As will beexplained in detail later, this arrangement of transducer imagingassemblies provides an improved, expanded, field of view for thediagnostic technician.

FIG. 6 is a side view of the pencil-sized transducer probe module 34shown in FIG. 5, especially configured for use in surgical anddiagnostic applications having limited access.

FIG. 7 is a plan view of the transducer probe 34 shown in FIG. 6 withthe distal end of the probe body being shown in partial cross section.The transducer probe 34 has a shaft 40 that is preferably cylindrical inshape. An acoustic lens 20 covers the lateral end adjacent the tip ofthe probe 34, and an acoustic lens 22 covers the distal end of the probe34. If desired, lenses 20 and 22 may be manufactured as a single lensmember having a right angle cross sectional configuration and made ofsilicon rubber or urethane polymer.

At the opposite end of the transducer probe module 34 is the couplingplug member 36, being preferably flat and rectangular in shape. It canbe seen in FIG. 7 that the plug 13 has a plurality of electrical contactpads 38 which connect to a corresponding plurality of traces on a flexcircuit leading to the transducer assembly at the distal end of theprobe 34, the details of which will be described hereinafter. When theplug 36 is connected to the receptacle 40 (FIG. 4), the electricalcontacts 38 on the plug member 13 make contact with the cable leads fromthe ultrasound system.

In the cutaway segment of FIG. 7, a thin film ground plane 42 isvisible, beneath which ground plane 42 a large plurality of flex circuittraces (not visible in FIG. 7) are positioned, such traces leading tothe lateral transducer stack assembly 48 which creates a 90° field ofview 70. As will be fully described in connection with other drawingfigures, a second flex circuit and an associated ground plane areprovided for the transducer stack assembly 46 at the end of the probeshaft 40, producing a 90° field of view 68. The respective 90° fields ofview 68, 70 preferably overlap one another to produce a combined fieldof view approaching 180°.

In FIG. 8, the housing shaft 40 of the transducer probe module 34 isshown in cross section, the shaft 40 providing a housing for theinterior components of the transducer probe 34. At the distal end ofshaft 40, a Radel™ plastic nose piece 64 is affixed, nose piece 64mounting the acoustic lenses 20, 22. Such construction permits theacoustic lenses 20 and 22 mounted to the nose piece 64 in a separateoperation, and the assembled nose piece and lens combination may then beconveniently and easily fixed to the distal end of shaft 40, oriented inthe proper relationship to the orientation of the plug 36.

Within the cross sectional view of FIG. 8, the exposed end portion ofthe transducer probe 34 shows the positions of the front lookingtransducer array 46 and the lateral looking transducer array 48. Forconvenience, in this description, the front looking transducer arraystack will be referred to hereinafter as the front stack 46, while thelateral looking transducer array stack will be referred to as thelateral stack 48.

In FIG. 8, it will be noted that the lateral lens 20 is angled slightlyinwardly toward the end of probe 34, such that its field of view 70overlaps the field of view 68 produced by the front stack 46. Asmentioned, the front and lateral stacks operate on the principle ofphased array acoustic imaging which produces a generally trapezoidalshaped field of view of approximately 90°, such that the combined fieldof view as shown in FIG. 8 will approximate 180°. Also as mentionpreviously, using trapezoidal sector imaging, a field of viewapproaching 110° is possible, thereby making the combined field of viewfor the FIG. 8 configuration of the present invention approaching 220°as a practical limit.

Each transducer stack 46, 48 is preferably comprised of sixty-fourpiezoelectric transducer elements, and in FIG. 8, such elements would beelongated elements having a direction into the page across the front andlateral side at the distal end of probe 34. In order to provideelectrical connection to each of the sixty-four transducer elements ofeach front and lateral stack 46, 48, multiple trace flex circuits may beused. For example, a flex circuit 44 with sixty-four individual paralleltraces are connected to the sixty-four transducer elements of thelateral stack 48, and the traces on the flex circuit 44 are led towardthe connector end of the probe 34 in a manner to be describedhereinafter.

The flex, or flexible, circuit 44 may be, for example, anyinterconnecting design used in the acoustic or integrated circuit field.A suitable flexible circuit is manufactured by Sheldahl of Northfield,Minn. The flexible circuit is typically made of polyimide material,typically KAPTON™, upon which a plurality of copper signal traces arebonded, the traces carrying the signals for exciting individualtransducer elements. The individual piezoelectric transducer elementsare connected to the ends of the copper signal traces, each signal traceterminating at a center pad, also preferably formed of copper, uponwhich center pad each transducer element is disposed and connected. Theinterconnect center pads may be gold plated to improve the contactperformance. Preferably, the center pads are coextensive in size withthe electrode of the transducer element.

The transducer elements of the front and lateral looking stacks aresequentially arranged in the direction parallel with the plane of thepaper as shown by arrows Y and X in FIG. 8. Preferably, there aresixty-four elements in each transducer array, and each transducerelement of the array disposed on the front and lateral stacks 46, 48will have a width as represented by the arrow W in FIG. 16.

To establish a transmission line effect for the traces on flex circuit44, to protect the traces on flex circuit 44 from the induction ofnoise, either from the environment or from the body under investigation,and to minimize cross talk or other effects due to coupling of signalsfrom the traces, a ground plane 42, insulated from the signal traces, isconnected to system ground and covers the traces all the way up to theconnection of the individual traces to the transducers on the frontstacks 46. In FIG. 8, the ground plane 42 is shown cut away in order toillustrate the routing of signal traces on flex circuit 44 leading tothe lateral stack 48. In FIG. 8, only the lateral stack flex circuit 44is visible. The front stack flex circuit is beneath.

FIG. 9 illustrates the lateral acoustic transducer stack subassemblycomprising the lateral stack 48, the flex circuit 44, the ground plane42, and, in phantom, the backing block 50 seen in FIGS. 10 and 11.

In FIG. 10, a right edge view of the subassembly shown in FIG. 9, itwill be observed that the backing block 50, against which the flexcircuit 44 lies, has a back edge 52. The back side 54 of flex circuit 44is a thin dielectric film upon the other side of which the traces offlex circuit 44 are formed.

FIG. 11 is a rear view of the lateral acoustic subassembly shown in FIG.9, and in this view, the triangular wedge shape of backing block 50 isobservable. The back edge 52 of backing block 50 is seen to define thehypothenuse of the right triangular cross section of backing block 50.The piezoelectric elements of lateral stack 48 are represented in FIG.11 on the right side of backing block 50 as shown.

It will be understood that, since the plane of the lateral stack 48 isto be tilted slightly inwardly at the probe end, in order to keep theback edge 52 at a 45° angle, the lateral side of the wedge-shapedbacking block 50 will be slightly shorter than the rearward side.Maintaining the angle of back edge 52 at 45° is essential for purposesof mating with the backing block of the front looking acousticsubassembly to be described with reference to FIGS. 12-14.

Alternatively, as mentioned, fields of view up to about 110° arepossible, such that the front stack 46 and lateral stack 48 may bearranged orthogonally. One advantage of this configuration is that thebacking blocks 50, 58 can be manufactured identically.

FIG. 12 illustrates the front acoustic transducer stack subassemblycomprising the front stack 46, the flex circuit 56, the ground plane 45,and, in phantom, the backing block 58 seen in FIGS. 13 and 14.

In FIG. 13, a right edge view of the subassembly shown in FIG. 12, itwill be observed that the backing block 58, against which the flexcircuit 56 lies, has a back edge 62. The back side 60 of flex circuit 56is a thin dielectric film upon the other side of which the traces offlex circuit 44 are formed.

FIG. 14 is a rear view of the front acoustic subassembly shown in FIG.12, and in this view, the triangular wedge shape of backing block 58 isobservable. The back edge 62 of backing block 58 is seen to define thehypothenuse of the right triangular cross section of backing block 58.The piezoelectric elements of front stack 46 are represented in FIG. 14at the top of backing block 58 as shown.

FIG. 15 is a composite drawing showing the internal workings of theprobe 34 absent the shaft housing 40, the nose piece 64, and the lenses20, 22. In this figure, the angular relationship between the front stack46 and the lateral stack 48 will be appreciated.

FIG. 16 is a left side view of the arrangement shown in FIG. 15. In thisfigure, the elongated piezoelectric transducer elements making up thelateral stack 48 are visible, and their lengths are shown relative tothe thickness of the backing block 50. The front stack 46 is shown inedge perspective in FIG. 16, but has the same physical appearance inplan view as that shown for lateral stack 48.

Referring to the group of FIGS. 8-16, the front looking acousticsubassembly of FIGS. 12-14 is similar in design to the lateral acousticsubassembly of FIGS. 9-11, except that the front stack backing block 58is substantially the mirror image of the lateral backing block 50.Additionally, the signal traces of the front stack flex circuit 56 donot turn 90°. Instead, they extend upon the flex side of the backingblock 58 and over the top surface of backing block 58 as can be seen inFIG. 13.

The front stack 46 and lateral stack 48 are assembled togetherback-to-back to form the transducer assembly shown in FIGS. 8, 15, and16. In particular, the angular back edge 62 of the front stack 46 andthe angular back edge 52 of the lateral stack 48 are mated together sothat both angular surfaces are in surface contact along their entirelength. Both angular back edges 52 and 62 are preferably machined toprovide precision flat surfaces for bonding the backing blocks 50, 58together. Preferably, an adhesive, more preferably an epoxy adhesive, isfirst applied to the angular back edge 52 of the lateral stack 48. Thefront stack 46 is then positioned in place with angled edges 52 and 62in contact, and the front stack 46 is slid along the mutually engagingsurfaces 52 and 62 until a predetermined alignment of the two transducerstacks is achieved. When coupled in this way, a single square orrectangular backing block results. As so assembled, the emittingsurfaces of the transducer arrays of the front and lateral stacks 46, 48are substantially perpendicular to one another.

Referring back to FIG. 8, the front and lateral stacks 46, 48, afterassembled and bonded together, are placed in the housing shaft 40 withthe emitting surfaces of the transducer arrays exposed. The acousticlenses or windows 20, 22 are fixed at one end and at a position on oneside of the nose piece 64. The nose piece 64, with the lenses 20, 22affixed thereto is then placed in the end of housing shaft 40. Bondingof the lenses 20, 22 to the nose piece 64, and bonding of the nose piece64 to housing shaft 40 may be effected by epoxy bonding or otheradhesive or cohesive bonding, sonic weld bonding, or any other bondingtechnique which tightly seals the connections.

Because the invention preferably employs trapezoidal sector imagingformat for each transducer stack, it is preferable to fire each arrayindependently temporarily. Otherwise, the circuitry required to operateboth (or all) arrays simultaneously becomes quite complicated.Considering that the backing blocks 50 and 58 are highly attentive, i.e.substantially absorptive of ultrasound energy radiated in its directionaway from an object of interest, a synergistic effect is realized byplacing the backing blocks with their back edges bonded together. Thatis, the active array has its own backing block plus the other backingblock to absorb ultrasound energy directed behind the array, therebyminimizing acoustic artifacts in signals supplied to the ultrasoundimaging system.

In a preferred embodiment, each transducer element has a width W (seeFIG. 16) of about 3 millimeters. Preferably, the diameter of the housingshaft 40 is about 10 millimeters. Also, preferably, each signal trace ofthe flex circuits 44, 56 has a width of about 0.05 millimeters and thespacing between signal traces is about 0.05 millimeters. Since eachtransducer array has sixty-four transducer elements, the flex circuits44, 56 will each have sixty-four signal traces.

In a preferred embodiment, the backing blocks 50, 58 are formed of afilled epoxy comprising Dow Corning's part number DER 332 treated withDow Corning's curing agent DEH 24 and has an aluminum oxide filler. In apreferred embodiment, the piezoelectric layer is composed of leadzirconate titanate (PZT). However, it may be formed of compositematerial or polymer material (PVDF).

FIG. 17 is a cross section of the transducer probe 18 in theinterconnect area within shaft 40, the view taken along the lines 17--17in FIG. 2.

As viewed in FIG. 17, the preferred cross sectional configuration forthe shaft 40 is shown to be cylindrical having an outside diameterpreferably of about 9.8 millimeters and an inside diameter preferably ofabout 8.3 millimeters.

Although a pencil-sized ultrasound transducer employing the concepts ofthe present invention may be structured in a variety of configurations,the accompanying drawings show two physical embodiments, and thedescription to follow is also limited to these two embodiments. However,it will be understood that many different physical body configurationsmay be envisioned for implementing the pencil-sized ultrasoundtransducer.

In accordance with a first embodiment, the self-contained transducerassembly of FIG. 2 requires, within the transducer probe 18, terminationof multiple coaxial conductors within cable 14, such cable terminationsbeing required to electrically connect the coaxial conductors of cable14 to individual transducer elements via the aforementioned flexcircuits.

The embodiment of FIGS. 4 and 5, on the other hand, terminate themultiple coaxial conductors in cable 14 within receptacle 40, and thecoupling plug member 36 need only be provided with a plurality ofelectrical contact pads 38 to make appropriate connections to themultiple coaxial conductors of cable 14 within receptacle 40. However,the transducer probe module 34 shown in FIG. 5 would thus require,within housing shaft 40, multiple connections between the flex circuits44 and 56 coupled to the front and lateral stacks 46 and 48, and theelectrical contact pads 38. To accomplish this, the coupling member 36takes the form of a printed wiring board having the electrical contactpads 38 being carried through the printed wiring board to within thehousing shaft 40 for connection with the flex circuitry.

Accordingly, in the description to follow, both the self-contained unitof FIG. 2 and the modular configuration of FIGS. 4 and 5 will bedescribed separately insofar as connection to the cable 14 to the frontand lateral stacks 46, 48 are concerned.

As mentioned, FIG. 17 is a cross section of the self-containedpencil-sized ultrasound transducer assembly of FIG. 3, and thereforeshows sixty-four 40-gauge coaxial conductors 72 of the system cable 14on one side of an interconnect printed wiring board 74 (having a widthof approximately 7.5 millimeters), and the flex circuit arrangement 73on the opposite side of the printed wiring board 74.

Details of the connection between the multiple coaxial conductors 72 andthe flex circuit arrangement 73 will become clearer in the descriptionto follow. The general configuration of the flex circuit arrangement 73can be appreciated by reference to FIG. 17, in which a 0.0125 millimeterthick stiffener 78 lies on top of the interconnect printed wiring board74 providing a support for the flex circuit 56 with its ground plane 45being on top. The interconnect printed wiring board 74 has a number ofinterconnect pads 84 which are mechanically and electrically connectedto corresponding ends of the traces on flex circuit 56 by standardsolder bridges 76, typically on 0.75 millimeter centers.

Since the view seen in FIG. 17 is forward of the transducer probe 18shown in FIG. 2, the termination of sixty-four of the coaxial conductors72 will have been interconnected with their corresponding traces on flexcircuit 44 rearwardly of the cross sectional position. It will beunderstood, however, that a similar arrangement as that shown in FIG. 17would be visible toward the proximal end of transducer probe 18 withsixty-four additional coaxial conductors 72 in the space above flexcircuit arrangement 73, and with a corresponding flex circuitarrangement positioned on the underside of a second interconnect printedwiring board 74, again rearwardly within transducer probe 18.

FIGS. 18 and 19 show, respectively, the coaxial conductor interconnectside 75 and the flex circuit interconnect side 77 of interconnectprinted wiring board 74 shown in FIG. 17. As mentioned, two of theseinterconnect printed wiring boards 74 are required, each providing aninterconnection between sixty-four coaxial conductors and associate flexcircuit arrangements for the two separate front and lateral stacks.FIGS. 18 and 19 thus show only one of such printed wiring boards.

Alternatively, a single long printed wiring board (not shown) may bepreferred, on which all 128 coaxial conductors connect with 128 traceson the flex circuits.

Both sides of the printed wiring board 74 have ground plane copperlayers 49 and 51 on the coaxial and flex circuit sides 75, 77,respectively. On the coaxial conductor side 75, the ground plane copperlayer 49 is etched away in two locations for the placement of thirty-twocoaxial conductor interconnect pads 78, 80 at one edge of the printedwiring board 74. Representative coaxial conductors 82 are shownschematically in FIG. 18, the details of which will follow. A pair ofholes 76 is provided at the ends of printed wiring board 74 for aligningthe printed wiring board 74 with corresponding alignment holes (notshown) on the flex circuits. With alignment pins (not shown) passingthrough both sets of holes, precise alignment of the interconnect pads78 and traces on the flex circuits 44, 56 is achieved to ensure solidand reliable solder connections.

The flex circuit interconnect side 77 of printed wiring board 74 shownin FIG. 19 shows the sixty-four flex interconnect solder pads 84 allalong one edge of the printed wiring board 74 opposite the edge forconnection of the coaxial conductors. Not shown, but well understood byone of ordinary skill in the art, the circular shaped pads shown inFIGS. 18 and 19 represent via holes in the printed wiring board 74, thevia holes connected to intermediate traces within printed wiring board74 leading from the sixty-four coaxial conductor interconnect pads 78 tocorresponding ones of the flex interconnect solder pads 84.

FIG. 20 is a perspective view of a segment of the printed wiring board74 and the associated coaxial conductors 72 and flex circuit arrangement73 on opposite sides of the printed wiring board 74. In comparing FIG.20 with other figures, it should be noted that the acoustic stacks arelocated in the direction of arrow 81, and the cable en of thearrangement shown is in the direction of arrow 83.

Preferably, printed wiring board 74 is an epoxy-glass laminate with anetched copper layer bonded thereto forming interconnect pads 84 asdescribed in connection with FIG. 19. The flex circuit arrangement 73 isshown to have an exterior ground plane layer 45, spaced from the signaltraces 59 of flex circuit 56 by a dielectric spacer 86. The ground plane45 stops short of interfering with the individual traces 59 of the flexcircuit 56. The flex circuit 56 has a wrap around edge 57 wrapped aroundthe right edge (as seen in FIG. 20) of stiffener 78, the series oftraces 59 being precisely aligned with corresponding interconnect pads84 on the printed wiring board 74. Mechanical and electrical connectionsbetween the individual traces 57 and interconnect pads 84 are providedby a corresponding number of solder bridges 76.

The copper ground plane 45 has a lateral extension 47 wrapped around theend of stiffener 78 but spaced from the last interconnect pad 84 on theprinted wiring board 74. As seen in FIG. 19, the copper ground planelayer 51 of printed wiring board 74 extends the length of the board 74and lies adjacent both ends of the series of interconnect pads 84. Asshown in FIG. 20, the extension 47 of ground plane 45 is, like the wraparound edge 57 of flex circuit 56, wrapped around the stiffener 78, anda rather large solder bridge 90 mechanically and electrically connectsthe ground plane extension 47 of the flex circuit to the ground planecopper layer 51.

In FIG. 21, a representative number of coaxial conductors 72 are shownlying on the termination, or interconnect, side 75 of the printed wiringboard 74. Each coaxial conductor 72 comprises an outer conductorinsulator 92, a conductor shield 94, an inner conductor dielectric 96,and a signal conductor 98. The conductor shield 94 of each coaxialconductor 72 is soldered at 102 to the ground plane 49 (see FIG. 18),and the signal conductor 98 of each coaxial conductor 72 is soldered toa corresponding termination/interconnect pad 80 (see FIG. 18) at soldertermination 100.

Reference is now made to FIGS. 22-27 showing the interconnection betweenflex circuits from the front and lateral stacks 46, 48 to a printedwiring board 110 leading to the coupling plug member 36 of the modulartransducer probe 34 shown in FIG. 5.

FIG. 22 illustrates in more detail the electrical contact pads 38 on thecontact pad side of coupling plug member 36. In this figure, the flexcircuit 44 from the lateral stack 48 is shown to be connected atsixty-four places along one edge of the printed wiring board 110. Asseen in FIGS. 22, 23, and 25, sixty-four flex circuit interface pads 112are arranged along the edge of printed wiring board 110. The flexcircuit 44 is wrapped around a stiffener (not shown) in a manner similarto that shown and described in connection with FIG. 20, such thatsixty-four solder bridges 114 electrically and mechanically interconnectbetween the flex circuit traces and the printed wiring board 110.

FIG. 23 is a side view of the arrangement shown in FIG. 22, this figureshowing the lateral flex circuit arrangement 71 coupling the printedwiring board 110 to the lateral stack 48, and the front stack flexcircuit arrangement 73 coupling the printed wiring board 110 to thefront stack 46.

FIG. 23 also shows the flex circuit stiffener 78 (cf FIG. 17) for frontstack flex circuit arrangement 73, and a corresponding flex circuitstiffener 87 for the lateral flex circuit arrangement 71. The copperground plane layers 53 and 55 for the contact pad side and back side ofprinted wiring board 110 shown in FIGS. 22 and 24, respectively, extendend-to-end of printed wiring board 110 with the exception that it isetched away for isolation from the contact pads 38 and the strip ofinterface pads 112, 120, 116, and 122 on both sides of printed wiringboard 110.

FIG. 24 is a representation similar to that of FIG. 22, but showing thefront stack assembly, i.e. flex circuit arrangement 73 connecting thepiezoelectric elements of front stack 46 to sixty-four correspondingprinted wiring board interconnect pads 116 soldered to the traces offlex circuit 56 at solder bridges 118.

FIGS. 25-27 show the printed wiring board 110 layout and constructionwithout the flex circuit arrangements attached. The printed wiring board110 is preferably a multilayer printed wiring board with 6 layers eachabout 0.8 millimeters thick. This configuration for the printed wiringboard 110 will permit reasonable sized internal copper traces in the 6layers to route the signals from flex circuit interface pads 112 and 116to corresponding contact pads 38 on coupling plug member 36. Thecircular pads shown connected to flex circuit interface pads 112 and116, and the series of circular pads 120 and 122 on the respectiveopposite sides of printed wiring board 110 represent via holes forconnecting the copper traces on the layers of printed wiring board 110between the interface pads 112, 116 to the electrical contact pads 38.

The embodiments of the invention described to this point involve a pairof ultrasound transducer arrays arranged at the distal end of apencil-sized housing and having a front field of view and a lateralfield of view which, when combined, provide an extended angular field ofview of approximately 180°. In the front looking and lateral lookingbi-stack transducer arrangement shown for example in FIG. 8, the centerof the image produced by the transducer is directed 45° to the port sideof the transducer. While this may be beneficial in observing, forexample, the walls of an organ into which the pencil-sized transducer isinserted, in other applications, a 180° field of view having a centerdirected forwardly of the transducer may be preferred. FIGS. 28-30provide such an embodiment.

In FIG. 28, a housing shaft 130 mounts, at its end, a nose piece 132mounting a unitary lens member comprising lens 138 and 142, behind whichare positioned a port side looking ultrasound transducer stack 136 and astarboard side looking ultrasound transducer stack 140, respectively. Inthis figure, it should be observed that the fields of view 137, 139 forthe stacks 136, 140 are greater than 90°. As a result, even with anoverlapping of the fields of view 137, 139, the combined field of viewis greater than 180°, a practical limit being about 220°.

This construction results in a centerline of the combined field of viewto be forward of the distal end of the transducer probe, defining afront looking bi-stack transducer 129.

The construction of the front looking bi-stack transducer is madepossible by the provision of a pair of backing blocks 146, 152 havingtheir back edges 148,150 bonded together along a centerline of thehousing shaft 130. A flex circuit 134 is shown in FIG. 29 to feed theport side stack 136, while a flex circuit (not visible) feeds thepiezoelectric elements of the starboard stack 140. FIG. 30 shows thebackside 144 of flex circuit 134 and the shape and positioning of thebacking block 146. It will be appreciated by reference to the phantomlines in FIG. 29 that the mirrored construction of a starboard flexcircuit arrangement (not shown) will result in the back edges 148 and150 being in axial alignment with the housing shaft 130. All otherfunction and structural features common to the front and lateral lookingbi-stack transducer of FIGS. 8-15 equally apply to the front lookingbi-stack transducer of FIGS. 28-30. Accordingly, a full representationof the entire bi-stack arrangement of the front looking transducer isnot necessary.

One advantage of a front looking bi-stack transducer constructed asshown in FIGS. 28-30 is that both acoustic stack subassemblies areidentical, resulting in reduced manufacturing and assembly costs.

The pencil-sized ultrasound transducer according to the presentinvention is not restricted to only a bi-stack configuration. Any numberof transducer stacks may be combined in a physical layout to produce anydesired field of view range, including a field of view of 360°. For allpractical purposes, however, a 360° field of view would be neithernecessary nor practical, since part of the field of view would includethe body of the transducer itself causing acoustic reflections whichcould introduce unwanted artifacts in the signal representing the imageof the body being investigated.

One practical multi-stack transducer, however, is shown in FIGS. 31-37in which 3 transducer stack subassemblies are arranged orthogonal to oneanother at the imaging tip of the transducer 160. In FIG. 31, the frontlooking tri-stack transducer 160 comprises a housing shaft 162 fittedwith a nose piece 164 to which a 3-sided lens member is attached, thelens member comprising lenses 168, 172, and 176. Behind lenses 168, 172,and 176, are corresponding transducer array stacks 166, 170, and 174.The generally trapezoidal shaped field of view patterns for the threetransducer stacks 166, 170, 174 are shown as fields of view 178, 180,and 182, respectively. Since each trapezoidal field of view is shown toexceed 90°, even with overlapping the fields of view as shown, the totalcombined field of view for the front looking tri-stack transducer 160 isgreater than 270°, a practical limit being 330°.

To construct the front looking tri-stack transducer 160, two identicallateral acoustic stack subassemblies are required as shown in FIGS.32-34. FIG. 32 shows the port side lateral transducer stack 166 beingfed by a flexible circuit 184. The flex circuit 184 is supported by abacking block 186 which has two machined back edge surfaces 188 and 190,as best seen in FIGS. 33 and 34.

The front looking acoustic stack subassembly is shown in FIGS. 35-37.The front looking stack 170 is fed by a flex circuit 196 which flaresoutwardly to connect with the individual transducer elements of thestack 170.

For case of illustration the required ground planes for the flexcircuits in FIGS. 31-37 are not shown.

As best seen in FIGS. 36 and 37, a triangular shaped backing block 191supports the front looking acoustic stack 170 and has machine surfacedback edges 192 and 194. In assembling the tri-stack transducer, the pairof identical lateral acoustic stack subassemblies of FIGS. 32-34 areassembled back-to-back with their back edges 188 in surface contact andbonding together. The front acoustic stack of FIGS. 35-37 is thenbrought into assembly with the lateral acoustic stack subassemblies withthe machined edges 192 and 194 in surface contact with and bonding tothe corresponding back edges 190 of the lateral acoustic stacksubassemblies.

As additional background information, a review of some ultrasoundimaging basics follows, particularly directed to a method for generatingultrasound images from two (or more) ultrasound stacks, both (all) onone plane.

GENERATING ULTRASOUND ENERGY: Very small thickness variations ofpiezoelectric crystal can be caused by subjecting it to an electricalfield across its thickness. The appropriate electrical signal toelectrodes on opposite surfaces of the crystal will cause ultrasonicenergy to be generated. This energy is transferred into the object ofinterest (e.g., a human body) by mechanical coupling. Piezoelectriccrystals can convert electrical signals into acoustic energy and canalso convert intercepted acoustic energy back into electrical signals.

ULTRASONIC BEAM FORMATION: The ultrasound energy from a linear array ofpiezoelectric crystals can be concentrated on a specific structure inspace (azimuth and range) by controlling the times at which the crystalstransmit (see FIG. 39). The circuitry which controls the transmittingprocess is, in general, incorporated into the imaging system; theprocess is called beamforming because it can cause the transducer toemit radial "beams" of acoustic energy into an object, such as a humanbody.

At a particular instant of time when the ultrasound energy originatingfrom the multitude of crystals converges on a structure of interest, areflection occurs having unique properties, relative to reflections fromits surroundings, due to the differences in acoustic properties of thestructure relative to its surroundings. The structure effectivelybecomes the source for a spherical "front" of ultrasound energy whichradiates in all directions; this energy is intercepted by eachindividual piezoelectric crystal in the linear array.

RECEPTION OF ULTRASOUND ENERGY FROM THE STRUCTURE: The amount of energyand the time at which it is received by each crystal is determined bythe crystal location (distance and angle) relative to the reflectivestructure. By introducing fin appropriate delays and amplifications intoin the electrical signal path from each crystal, then combining thesignals, a reinforced electrical representation of the structure can begenerated.

SCANNING THE IMAGING FIELD: One common method of acquiring the datarequired to reconstruct an image of structures within the body is totransmit one beam, or line, using all of the piezoelectric crystals inthe array as transmitters, then to receive reflected ultrasound energyusing all the piezoelectric crystals as receivers. The amplificationfactors and the delays introduced into the data stream from eachreceiver is optimized to observe structure where the transmitted beamwas focused. Upon reception of all the data for one beam, the next beamis transmitted into the body along a slightly different radial path, thereceivers optimized for that beam, etc. This sequential scanning of thefield with transmitted beams, together with the corresponding receivingactivity, causes the entire field of view of about 90° degrees to becovered.

DISPLAY OF THE STRUCTURE: A pictorial representation of a structure canbe generated by manipulating the data before sending it to a rasterdisplay (cathode ray tube or liquid crystal display). The image isgenerated from received data for each ultrasound line (beam) which istransmitted; the radial pattern of diverging ultrasound lines leads to atrapezoidal imaging pattern of the structures encountered by theultrasound beams. To generate the image, a regular sequence of beams aregenerated from one side of the volume of interest to the other side.

NORMAL ULTRASOUND FORMAT: Generally, the transducer incorporates alinear array of individual and independent piezoelectric crystals; theimage generated is trapezoidal in shape.

GENERATING AN IMAGE USING MORE THAN ONE TRANSDUCER ARRAY STACK: If twotransducer stacks radiating into the same plane are orthogonal to eachother, one of two methods can be used to generate an image whichdisplays structure from more than the normal 90 degree field of view.Each method addresses the potential ambiguity which can be caused byenergy from one stack intercepted by both.

The first method depends on displaying sequentially the independentlygenerated image from each stack. With reference to FIGS. 38-40, onedisplay image represents the structure in the field of view of lateralstack 48, while another display image represents the structure in thefield of view of front stack 46. Since alternate images, or frames, aregenerated and displayed at different times, there is no ambiguity ofdata from the receivers; data as a result of the energy transmitted bylateral stack 48 is not detected by front stack 46, because front stack46 is "blind" during the interval of time that lateral stack 48 is beingused, etc.

The first method may be performed using the block diagram and solidlined circuit paths of FIG. 38 which shows a pair of orthogonallydisposed transducer array stacks, lateral stack 48 and front stack 46.An image sequencing transmit beamformer 200, through transducerselection and control block 202, sends appropriate signals to lateralstack 48 and front stack 46 to create independent and alternate beamscans of the respective fields of view. The field of view of lateralstack 48 includes objects 204 and 206, while the field of view of frontstack 46 includes objects 206, 208, and 210. A receive beamformer imagesequencer 209 alternately presents the independently generated imagesfrom lateral stack 48 and front stack 46 to a display 214 through adisplay processor 212. Display processor 212 effects desired displaycharacteristics such as brightness, image and motion enhancement, color,etc.

The display 214 thus displays objects 204 and 206 on the left side ofthe display screen and objects 206, 208, and 210 on the right side ofthe display screen. Although object 206 is displayed in both screenpresentations, each object in each display half is scanned withtransmitted energy, and the reflected energy is analyzed, all by thesame transducer stack. That is, the circuitry for lateral stack 48 neverprocesses reflected acoustic energy originating from front stack 46, andvice versa. In this respect, the presentation on the display monitor 214is not unlike the imaging of independent transducer stacks, the onlydifference being that the electronics of FIG. 38 time shares the twoimage generating transducer stacks and presents the resulting imagesside-by-side on a display monitor.

As to the second method, reference is now made to FIGS. 39 and 40 inwhich FIG. 39 shows a transducer 222 generating a sequence of transmitbeams 224 from the lateral-facing transducer stack 48 and a continuingsequence of transmit beams 224 from the front looking transducer stack46, thereby forming a continuous 180° field of view 226. The secondmethod involves sequentially transmitting ultrasound beams 224 into thebody from the bottom to the top of lateral stack 48, then from the leftto the right of front stack 46. The beamformer thus causes the lineararrays of piezoelectric crystals to generate ultrasound beams 224 whichare transmitted into the body over an angle on the order of 180 degrees.

As illustrated in FIG. 40, reflected ultrasound energy 230 fromstructure 206 within the body, regardless of whether the transmittedsource of acoustic energy is from lateral stack 48 or front stack 46, islikewise intercepted by individual piezoelectric crystals in bothstacks. By optimizing the receiver amplifications and delays, takinginto account the geometry of the two stacks, a receive data stream usingpiezoelectric crystals in both stacks is thus acquired.

The beam sequencing method just described may be implemented using theblock diagram and dashed line circuit paths shown in FIG. 38, i.e., thetransducer selection and control block 202 is connected through thedashed lines instead of the solid lines in the figure. The field of viewpattern shown in FIG. 38 is replaced by the field of view pattern shownin FIG. 39 in this second method. The transducer selection and controlblock 202 thus effects the beam generation sequence as describedstarting with the bottom transducer element of lateral stack 48 andending with the right most transducer element of front stack 46 in acontinuous sequence of beamforming to create the approximately 180degree field of view. As opposed to sequencing alternating images fordisplay on display monitor 214, circuit blocks 216 and 218 perform thetransmit and receive beamforming with each field of view defined by acontinuous sequencing of transmitted beams 224 across both stacks.

Employing this second method, a beam sequencing transmit beamformer 216,through transducer selection and control block 202, sends appropriatesignals to lateral stack 48 and front stack 46 to create continuous beamscans across the two stacks. The transmitted beams from lateral stack 48impinge objects 204 and 206, while the transmitted beams from frontstack 46 impinge objects 208 and 210. In the second method, as seen inFIG. 39, it will be observed that the transmission fields of view oflateral stack 48 and front stack 46 do not overlap, resulting in apresentation on display monitor 222 of the entire 180 degree field ofview as if a single transducer array stack generated it.

In the beam sequencing receive beamformer 218, it will be observed fromFIG. 40 that the signal received from the right most crystal element offront stack 46 must have the most gain and the least delay of all of thetransducer elements in front stack 46, while the signal from the leftmost crystal element of front stack 46 must have the least gain and mostdelay of all the transducer elements in front stack 46 in order todefine a received reflected ultrasound beam from structure 206. Displayprocessor 220 effects desired display characteristics such asbrightness, image and motion enhancement, color, etc.

The display 222 thus displays objects 204, 206, 208, and 210 as if asingle 180 degree field of view was generated by a single transducerstack.

FIGS. 38-40 have dealt with the transmission and receiving of ultrasoundenergy from two stacks substantially orthogonally disposed. As presentedherein, an extension of the circuit of FIG. 38 and the analysis of FIGS.38-40 involving more than two transducer stacks would apply and bereadily evident to a person of ordinary skill in the art afterunderstanding the details of these figures. In this connection,reference is made to U.S. patent application Nos. 08/286,658,08/432,615, and 08/434,160, and to PCT International Publication No. WO96/04568, all of which are incorporated herein by reference. Thesereferences explain in great detail transmit and receive beamformingtechnology. It is presumed that the person of ordinary skill in the artto which the present invention pertains is familiar with and can applythe principles set forth in these references of prior art whereappropriate and necessary in the understanding of the present invention.

While only certain embodiments of the invention have been set forthabove, alternative embodiments and various modifications will beapparent from the above description and the accompanying drawing tothose skilled in the art. For example, for the probe module 34 of FIG.5, coaxial conductors may be used to connect the contact pads 38 to theflex circuits 44, 56, instead of using printed wiring board connections.Alternatively, the printed wiring board 110 may serve to directlyconnect all transducer elements to respective contact pads on thecoupling plug member 36 without employing flex circuits. These and otheralternatives are considered equivalents and within the spirit and scopeof the present invention.

What is claimed is:
 1. An ultrasound transducer assembly, comprising:ahousing having a distal end, a proximal end and an axis through thedistal end and the proximal end; a first phased array transducerarranged at said distal end for acquiring an ultrasound image forward ofsaid distal end in an imaging plane parallel to or coincident with theaxis of the housing; and a second phased array transducer arranged atsaid distal end for acquiring an ultrasound image laterally of saiddistal end within the same imaging plane.
 2. The ultrasound transducerassembly as claimed in claim 1, wherein:each said first and secondphased array transducer comprises a linear arrangement of piezoelectrictransducer elements; and said first and second phased array transducersare positioned substantially perpendicular to one another at said distalend.
 3. The ultrasound transducer assembly as claimed in claim 2,wherein said housing is of an elongated pencil-sized configuration. 4.The ultrasound transducer assembly as claimed in claim 2, wherein saidhousing is of an elongated, cylindrical, pencil-sized configuration. 5.The ultrasound transducer assembly as claimed in claim 1, comprising amultiple conductor cable having a first end entering said housing andelectrically coupled to said first and second phased array transducers,and a second end terminated by a system connector for selectively makingconnection with an ultrasound system.
 6. The ultrasound transducerassembly as claimed in claim 1, comprising:a plug at said proximal end,said plug comprising electrical contacts; electrical conductors couplingsaid plug to said first and second phased array transducers; and whereinsaid plug is receivable in a receptacle attached by a cable to anultrasound system.
 7. The ultrasound transducer assembly as claimed inclaim 6, wherein:said plug at said proximal end is a printed wiringboard with electrical contact pads thereon for making electrical contactwith corresponding electrical contacts in the receptacle; and saidelectrical conductors are defined by a plurality of signal traces withinsaid printed wiring board connected to an interconnect printed wiringboard in said housing, and further defined by a plurality of signaltraces on a flex circuit connected from said interconnect printed wiringboard to said first and second phased array transducers.
 8. Theultrasound transducer assembly as claimed in claim 6, wherein:said plugat said proximal end is a printed wiring board with electrical contactpads thereon for making electrical contact with corresponding electricalcontacts in the receptacle; and said electrical conductors are definedby an extension of said printed wiring board.
 9. An ultrasoundtransducer assembly, comprising:a elongated pencil sized housing havinga distal end and a proximal end; a first phased array transducerarranged adjacent said distal end for acquiring an ultrasound image in afirst image plane and within a first field of view of about 90°; and asecond phased array transducer arranged adjacent said distal end foracquiring an ultrasound image in a second image plane and within asecond field of view of about 90°, said first image plane being coplanarwith said second image plane, and said second field of view overlappingsaid first field of view, resulting in a combined field of view of about180°.
 10. The ultrasound transducer assembly as claimed in claim 9,wherein:said elongated housing has an axis through the distal end andthe proximal end, and said first field of view is centered about adirection line at an angle of about 45° to one side of said axis in saidcoplanar image planes; and said second field of view is centered about adirection line at and angle of about 45° to the other side of said axisin said coplanar image planes.
 11. An ultrasound transducer assembly,comprising:a plurality of ultrasound phased array transducers mounted ona transducer probe, each comprising an array of transducer elementsarranged linearly along an array axis, said linear arrays being arrangedend-to-end and nonaxially aligned, each phased array transducer having afield of view defining an image plane; wherein the array axis of eachphased array transducer lies within its corresponding defined imageplane, said image planes of all said phased array transducers coincide;and each said phased array transducer has a field of view of about 90degrees, whereby a resulting combined field of view greater than 90degrees is produced.
 12. The ultrasound transducer assembly as claimedin claim 11, wherein:said plurality is two; said array axes of saidphased array transducers are oriented substantially perpendicular to oneanother; and the combined field of view is about 180°.
 13. An ultrasoundtransducer assembly, comprising:two independent imaging stacks eachcomprising an array of transducer elements, each imaging stack having acorresponding wedge-shaped backing block and defining a predeterminedfield of view when energized using a trapezoidal sector imaging format;and two independent conductor strips carrying signal traces forelectrical connection to corresponding ones of said transducer elements,each said conductor strip having a front surface and a rear surface,said signal traces being disposed on said front surfaces, and saidwedge-shaped backing blocks being disposed on said rear surfaces;whereby placing said conductor strips back-to-back positions saidwedge-shaped backing blocks side-by-side and produces overlapping fieldsof view.
 14. The ultrasound transducer assembly as claimed in claim 13,wherein said conductor strips are flex circuits.
 15. The ultrasoundtransducer assembly as claimed in claim 13, wherein said backing blocksare bonded together.
 16. An ultrasound transducer assembly for supplyingsignals to an ultrasound imaging system, comprising:a plurality ofacoustic transducer stacks each having a field of view forward of saidtransducer stack and a backing block rearward of said transducer stack,each said backing block being highly absorptive of ultrasound energyradiating rearwardly of said transducer stack to minimize acousticartifacts in signals supplied to the ultrasound imaging system from saidultrasound transducer assembly; and bonding material bonding saidplurality of backing blocks together to further suppress acousticartifacts in signals supplied to the ultrasound imaging system.
 17. Anultrasound transducer module, comprising:a housing having a distal end,a proximal end and an axis through the distal end and the proximal end;a first transducer array arranged at said distal end for acquiring adiagnostic image forward of said distal end in an imaging plane parallelto or coincident with the axis of the housing; a second transducer arrayarranged at said distal end for acquiring a diagnostic image laterallyof said distal end within the same imaging plane; a plug member at saidproximal end, said plug member being electrically coupled to said firstand second transducer arrays and being receivable in a receptacleattached by a cable to an ultrasound system.
 18. The ultrasoundtransducer module as claimed in claim 17, wherein said housing is of anelongated, cylindrical, pencil-sized configuration.
 19. An ultrasoundtransducer assembly, comprising:a elongated pencil sized housing havinga distal end and a proximal end; a first steerable transducer arrayarranged adjacent said distal end for acquiring an ultrasound image in afirst image plane and within a first field of view of about 90°; and asecond steerable transducer array arranged adjacent said distal end foracquiring an ultrasound image in a second image plane and within asecond field of view of about 90°, said first image plane being coplanarwith said second image plane, and said second field of view overlappingsaid first field of view, resulting in a combined field of view of about180°; wherein: said elongated housing has an axis through the distal endand the proximal end, and said first field of view is centered about adirection line at an angle of about 45° to one side of said axis in saidcoplanar image planes; and said second field of view is centered about adirection line at and angle of about 45° to the other side of said axisin said coplanar image planes.
 20. An ultrasound transducer assembly,comprising:an elongated pencil sized housing having a distal end and aproximal end; a first transducer array arranged adjacent said distal endfor acquiring an ultrasound image in a first image plane and within afirst field of view of about 90°; a second transducer array arrangedadjacent said distal end for acquiring an ultrasound image in a secondimage plane and within a second field of view of about 90°, said firstimage plane being coplanar with said second image plane, and said secondfield of view overlapping said first field of view; and a thirdtransducer array arranged adjacent said distal end for acquiring anultrasound image in a third image plane and within a third field of viewof about 90°, said third image plane being coplanar with said firstimage plane, and said third field of view overlapping said second fieldof view, resulting in a combined field of view of about 270°.
 21. Theultrasound transducer assembly as claimed in claim 20, wherein:saidelongated housing has an axis through the distal end and the proximalend, and said first field of view is centered about a direction linealong said axis in said coplanar image planes; said second field of viewis centered about a direction line at and angle of about 90° to one sideof said axis in said coplanar image planes; said third field of view iscentered about a direction line at and angle of about 90° to the otherside of said axis in said coplanar image planes.
 22. A method ofmanufacture of an ultrasound transducer, comprising:providing a housinghaving a distal end, a proximal end and an axis through the distal endand the proximal end; arranging a first phased array transducer at saiddistal end for acquiring an ultrasound image forward of said distal endin an imaging plane parallel to or coincident with the axis of thehousing; and arranging a second phased array transducer at said distalend for acquiring an ultrasound image laterally of said distal endwithin the same imaging plane.
 23. The method as claimed in claim 22,wherein:each said first and second phased array transducer comprises alinear arrangement of piezoelectric transducer elements; and said firstand second phased array transducers are positioned substantiallyperpendicular to one another at said distal end.
 24. A method ofmanufacture of an ultrasound transducer, comprising:producing aplurality of ultrasound phased array transducers each comprising anarray of transducer elements arranged linearly along an array axis, eachphased array transducer having a field of view defining an image plane;and aligning the array axis of each phased array transducer to liewithin its corresponding defined image plane.
 25. The method as claimedin claim 24, wherein:said plurality of phased array transducers arelinear arrays arranged end-to-end and nonaxially aligned; said imageplanes of all said phased array transducers are oriented so as tocoincide; and each said phased array transducer has a field of view ofabout 90°, thereby producing a resulting combined field of view greaterthan 90°.
 26. The method as claimed in claim 25, wherein:said pluralityis two; said array axes of said phased array transducers are orientedsubstantially perpendicular to one another; and the combined field ofview is about 180°.
 27. A method of manufacture of an ultrasoundtransducer, comprising:providing two independent imaging stacks eachcomprising an array of transducer elements; assembling each imagingstack on a corresponding wedge-shaped backing block for defining apredetermined field of view when energized using a trapezoidal sectorimaging format; providing two independent conductor strips carryingsignal traces and electrically connecting said traces to correspondingones of said transducer elements, each said conductor strip having afront surface and a rear surface, said signal traces being disposed onsaid front surfaces, and said wedge-shaped backing blocks being disposedon said rear surfaces; and placing said conductor strips back-to-back toposition said wedge-shaped backing blocks side-by-side for producingoverlapping fields of view.
 28. The method as claimed in claim 27,wherein said backing blocks are bonded together.
 29. A method ofmanufacture of an ultrasound transducer assembly for supplying signalsto an ultrasound imaging system, comprising:providing a plurality ofacoustic transducer stacks each having a field of view forward of saidtransducer stack and a backing block rearward of said transducer stack,each said backing block being highly absorptive of ultrasound energyradiating rearwardly of said transducer stack to minimize acousticartifacts in signals supplied to the ultrasound imaging system from saidultrasound transducer assembly; and bonding said plurality of backingblocks together to further suppress acoustic artifacts in signalssupplied to the ultrasound imaging system.
 30. A method of manufactureof an ultrasound transducer, comprising:providing a elongated pencilsized housing having a distal end and a proximal end; arranging a firststeerable transducer array adjacent said distal end for acquiring anultrasound image in a first image plane and within a first field of viewof about 90°; and arranging a second steerable transducer array adjacentsaid distal end for acquiring an ultrasound image in a second imageplane and within a second field of view of about 90°; aligning saidfirst image plane coplanar with said second image plane, and said secondfield of view overlapping said first field of view, resulting in acombined field of view of about 180°.
 31. The method as claimed in claim30, wherein:said elongated housing has an axis, and said first field ofview is centered about a direction line at an angle of about 45° to oneside of said axis in said coplanar image planes; and said second fieldof view is centered about a direction line at and angle of about 45° tothe other side of said axis in said coplanar image planes.
 32. A methodof manufacture of an ultrasound transducer, comprising:providing anelongated pencil sized housing having a distal end and a proximal end;arranging a first transducer array adjacent said distal end foracquiring an ultrasound image in a first image plane and within a firstfield of view of about 90°; arranging a second transducer array adjacentsaid distal end for acquiring an ultrasound image in a second imageplane and within a second field of view of about 90°; aligning saidfirst image plane coplanar with said second image plane, and said secondfield of view overlapping said first field of view; arranging a thirdtransducer array adjacent said distal end for acquiring an ultrasoundimage in a third image plane and within a third field of view of about90°; aligning said third image plane coplanar with said first imageplane, and said third field of view overlapping said second field ofview, resulting in a combined field of view of about 270°.
 33. Themethod as claimed in claim 32, wherein:said elongated housing has anaxis through the distal end and the proximal end, and said first fieldof view is centered about a direction line along said axis in saidcoplanar image planes; said second field of view is centered about adirection line at and angle of about 90% to one side of said axis insaid coplanar image planes; said third field of view is centered about adirection line at and angle of about 90° to the other side of said axisin said coplanar image planes.